Most edible oils go through a refining operation of which the last processing step is deodorization where a by-product or distillate with Free Fatty Acids, i.e. FFA, is produced. Besides the FFA's the distillate also contains valuable components such as tocopherols and tocotrienols, i.e. vitamin E and antioxidants, other components are sterols and squalene, these components are mentioned as a group often known as micronutrients.
A current trend in the edible oil industry is to use certain enzymes. A suitable enzyme is phospholipase A to enable removal of phosphor containing components of the crude edible oil down to very low concentration, i.e. ppm levels. However, a side effect of this process will increase production of FFA, which increase will dilute the micronutrients in the deodorizer distillates even more.
In recent years some refiners have in their deodorization sections included a condensation zone at high temperature in known as double scrubbers. Double scrubbers are disclosed for example in U.S. Pat. No. 6,750,359. Double scrubbers could be used to withdraw a process stream enriched in micronutrients. However, use of a double scrubber arrangement may lead to significant loss of micronutrients in the FFA rich overhead stream. A significant limitation of such an approach is that the separation efficiency is linked to the operating conditions of the deodorizer, where the main function is to produce edible oil by of stripping by steam under vacuum.
Esterification of fatty acids with methanol to produce fatty acid methyl esters is known, and is most often practiced in industry in multiple steps using a strong acid, such as sulphuric acid as catalyst. One disadvantage of any methanol esterification is the equilibrium conversion limitation, overcome only by removing water produced by the reaction, but thereby also simultaneously removing methanol, which has to be recovered.
Using glycerol instead of methanol for the esterification, the FFA is transferred to glycerides instead of methylesters. Glycerol esterification of FFA has been described using different types of catalysts, such as ZnO or ZnCl2, or enzymatic or solid phase catalysts. Using a catalyst will impose capital and operating costs, as well as adding effluent streams, unacceptable for large-scale commercial production. Zink, for example is considered environmental toxic for aquatic organisms. Enzymatic glycerol esterification is disclosed by WO 2008/125574.
Processes to purify micronutrients may involve a number of processing steps such as vacuum distillation, esterfications, transesterfications, saponification, short path distillation, e.g. as disclosed in U.S. Pat. No. 7,368,583. Common for such process is that it is much preferred to have as feed stream to the processes a concentrated stream of micronutrients to decrease the size of the purification plant, increase the yield of micronutrients, but also to lower the cost of transportation bringing the feed stream to the purification facility.
One problem with vacuum distillation methods for concentration of tocopherol concentrates according to the known methods are the significant loss of tocopherols and sterols with the produced FFA rich distillate. One of the reasons for the loss of tocopherols, when removing free fatty acids from tocopherols, is their similar vapour pressures. Also, storage and further refining of tocopherols require special precautions since tocopherols are readily oxidized.
Accordingly, there is a clear need for a more specified process that allows micronutrients to be refined to higher extent.